1. Field of the Invention
This invention relates to integrated circuit manufacture and, more particularly, to an apparatus and method for electrically programming indicia upon and retrieving indicia from an integrated circuit (i.e., "die") helpful, for example, in identifying that die from among numerous die within a wafer and/or wafer lot, and also identifying when the die was manufactured and at which fabrication facility it was manufactured.
2. Description of the Related Art
An integrated circuit is often referred to as a die or chip. Henceforth, those terms are henceforth interchangeably used. A die generally contains several thousand active and passive devices formed on a monolithic substrate. Those devices are generally interconnected to form an overall circuit. Active devices include transistors, whereas passive devices include resistors and capacitors, for example.
A monolithic substrate, often referred to as a semiconductor wafer, may contain several hundred die arranged across the wafer. After the active and passive devices are formed and selectively interconnected, each die is then tested both visually and electrically. The die which fail testing may then be marked with a visually detected "imprint". For example, a typical marking involves placing an ink or laser mark on non-viable die as the die are tested across each wafer. Die which are not marked with a visually detectable imprint, can then be separated from the wafer and thereafter used. The electrical testing procedure can be undertaken at several dissimilar temperatures, and possibly before and after stressing the die by exposing the die to temperature cycles.
Die which pass testing and are removed from the wafer may then be sealed or encapsulated within a semiconductor package. Leads extending from the package are electrically connected to bonding pads on the die internal to the package. The process of packaging good die is often referred to as "assembly". A conventional assembly operation may draw die from anywhere across a wafer, or from any wafer within a set of wafers or wafer lot. Assembly may also draw die from wafers among several wafer lots.
FIG. 1 illustrates a conventional assembly operation, whereby a packaged die 10 may be drawn from a first wafer 12 within lot 14. For example, package die 10 may be derived from die location 16 of wafer 12 within lot 14. Alternatively, die 10 can be drawn from location 18 within possibly the same lot 14 or, as shown, from another wafer 20 within another lot 22. Thus, FIG. 1 depicts multiple locations 16 and 18 from which an electrically viable die 10 can be extracted. Yet further, die 10 can also be obtained from either the first wafer or possibly another wafer 24 of yet a third lot 26. The location 28 from which die 10 is extracted can be the same as location 16 of lot 14 but from an altogether different wafer and/or possibly an altogether different lot.
Co-mingling good die from various locations of a single wafer, from several wafers, and from several wafer lots is what typically occurs during the assembly operation. Unfortunately, whenever die among multiple wafers and multiple lots are co-mingled, traceability as to that particular die is lost. If a packaged die later proves unreliable in the field, it would be beneficial from the viewpoint of the manufacturer to identify from where the packaged die was derived. It would also be desirable to determine how and when the packaged die was manufactured. Such indicia could aid the manufacturer in improving the manufacturing process not only after the packaged die is shipped, but also possibly during tests of the packaged product before shipment.
Conventional techniques used to identify die are primarily limited to pre-assembly. That is, typical identification methods rely upon visual markings placed on the die. Unfortunately, after the die is encapsulated within a package, the visual markings are obscured. Any failure analysis needed for an inoperable packaged product requires the package be opened and the die destroyed. It would be desirable to avoid using visual identification techniques for identifying die manufacturing information since identification and tracing of die should extend after assembly. The desirous technique of non-destructive identification proves especially useful in analyzing test skews on a viable die before and after assembly. Knowing the effect of assembly and/or usage in the field, and the effect of those operations on a unique die would prove valuable to an integrated circuit manufacturer.